1. Field of the Invention
The present invention relates to an apparatus and a method of the apparatus and, particularly to, for example, a printing apparatus that corrects a signal from an analog encoder sensor used for conveyance control of a printing paper sheet and a correction method of the printing apparatus.
2. Description of the Related Art
As an information output apparatus for, for example, a word processor, a personal computer, a facsimile apparatus, and the like, a printer that prints any desired information such as characters and images on a sheet-like printing medium such as a paper sheet or a film is widely used.
Various methods are known as the printing method for the printer. An inkjet method has particularly received a great deal of attention because of its quietness and capability of noncontact printing on a printing medium such as a paper sheet and facilitating color printing. Especially, a serial inkjet printing apparatus for performing printing while reciprocally scanning a printhead that discharges ink in accordance with a print instruction in a direction crossing the printing medium conveyance direction is widely used in general because it is inexpensive and facilitates size reduction.
Such an inkjet printing apparatus (to be referred to as a printing apparatus hereinafter) implements image printing of higher resolution by decreasing the ink discharge amount per dot while raising the integration density of nozzles for discharging ink droplets. For higher quality printing, a printing technique using not only four basic color inks (cyan, magenta, yellow, and black) but also light inks of lower dye densities or spot inks such as red, green, and blue inks is used.
There is a fear that the printing speed lowers as the printing quality becomes high. This problem is dealt with by increasing the printing paper sheet conveyance speed by, for example, increasing the number of printing elements mounted on a printhead, improving the driving frequency of printing elements, and employing reciprocal printhead scanning.
For the purpose of simultaneously attaining a high printing medium conveyance speed and a high conveyance accuracy in a printing apparatus, recently, an encoder that outputs analog feedback signals of A- and B-phase sine waves having a phase difference of 90° is used in a detector for detecting the position and speed of a conveyance motor. In these analog feedback signals of sine waves, an offset representing a shift of an amplitude center voltage from a set value, or their amplitudes and phase difference vary. For this reason, conventionally, analog feedback signals are observed using special measurement equipment such as an oscilloscope, information on the offset, amplitudes, and phase difference are obtained, and the analog feedback signals are adjusted. Alternatively, a dedicated calculation circuit or memory is prepared, and correction is done in the circuit.
For example, according to Japanese Patent Laid-Open No. 2007-107886, a position error signal waveform and an A-phase signal waveform are measured by an encoder analysis device. An encoder error included in two analog encoder sensor signals, that is, an A-phase encoder signal and a B-phase encoder signal is calculated and stored in a non-volatile memory. On the other hand, a correction circuit reads out the encoder error from the non-volatile memory, and corrects the A-phase encoder signal and the B-phase encoder signal.
In addition, according to Japanese Patent Laid-Open No. 2002-199768, a detection circuit A/D-converts analog feedback signals from an encoder. A calculation unit obtains the offset between the A- and B-phase analog feedback signals and their amplitudes and phase difference based on the converted digital signals. The obtained offset, amplitudes, and phase difference are displayed on the display unit of a motor control unit or the display device of a numerical controller that is the host apparatus of the control unit. In addition, the quality of the feedback signals from the encoder is discriminated by comparing the obtained offset and amplitudes with reference values.
In both of Japanese Patent Laid-Open Nos. 2007-107886 and 2002-199768, however, a dedicated memory and a dedicated circuit that collects and analyzes encoder signals are needed to decide the parameters for correction. This leads to an increase in the circuit scale and an increase in the cost of the entire apparatus.